XMM-Newton Announcement of Opportunity: Policies and Procedures

3.1 Calibration Time

About 5% of XMM-Newton's observing time is required to maintain the calibration, to monitor the health of the instruments and to perform engineering observations. Calibration observations already foreseen at the time of the Announcement of Opportunity are called routine calibration observations and are published.

Calibration observations which could not have been foreseen at the time of the announcement of opportunity are called non-routine calibration observations. Whenever possible, targets required for non-routine calibration observations are selected without generating additional duplications or violations of data rights of accepted observations.